domain-driven-design

SKILL.md

Domain-Driven Design Framework

Framework for tackling software complexity by modeling code around the business domain. The greatest risk in software is not technical failure -- it is building a model that does not reflect how the business actually works.

Core Principle

The model is the code; the code is the model. Software should embody a deep, shared understanding of the business domain. When domain experts and developers speak the same language and that language is directly expressed in the codebase, complexity becomes manageable and the system evolves gracefully as the business changes.

Scoring

Goal: 10/10. Score a domain model by awarding 1 point per satisfied row of the Quick Diagnostic (7 rows) plus up to 3 points for depth: +1 if the Core Domain has a genuinely rich model (not just CRUD), +1 if invariants live inside aggregates rather than in services, +1 if the ubiquitous language is consistent across conversation, code, and tests. Bands: 9-10 = expert-readable names, explicit context boundaries with ACLs, small aggregates, behavior-rich entities, events for cross-aggregate flow, an identified Core Domain; 5-6 = some domain language but leaky boundaries or anemic objects; <=3 = technical naming, one model for everything, logic scattered in services. Report the score and the specific diagnostic rows failing.

Framework

1. Ubiquitous Language

Core concept: A shared, rigorous language between developers and domain experts, used consistently in conversation, documentation, and code. When the language changes, the code changes -- and awkward naming in code feeds back into refining the language.

Why it works: Ambiguity is the root cause of most modeling failures. When a developer says "order" and an expert means "purchase request," bugs are inevitable; a ubiquitous language forces every name in code to map to a concept the business recognizes and validates.